Present day communications technology is directed more and more to the use of optical fibers for signal transmission. Optical fibers have the undisputed advantage over wire or metallic transmission media of a far greater signal bandwidth transmission capability, but they have the physical disadvantage of being far more fragile than metallic wire. Thus, the handling and routing of optical fibers, whether singly or in ribbons and/or cables not only demands extreme care in handling, but, also, extra measures of protection for the fibers. In routing either cables or single fibers, it is imperative, for reliable signal transmission, that sharp bends in the fibers be avoided. Inasmuch as the laws of optics apply to such transmission, a too sharp bend in the fiber can and does results in signal loss by virtue of at least some of the transmitted light leaking out of the fiber at the bend. A too sharp, i.e., small radius, bend can also cause at least some further signal degradation if the bend introduces microcracks in the fiber, which reduce or impair the uninterrupted guiding of the optical signals. The small bend radiuses can also cause fiber breakage. Most optical fiber being made today is capable of resisting formation of such microcracks or breakage, but when the fiber is subjected to recurring external forces, the tendency toward cracking and/or breakage increases.
In most environments where optical fiber cables terminate in, for example, an office building or in other user premises, the individual fibers are separated out of the cable and directed, by means of connectors and patch panels, to the particular user or to the particular signal receiving and/or transmitting equipment. Thus, in a typical patch panel arrangement, the fibers are separated on one side of the multi-apertured panel, and connectors are affixed to the ends of the fibers. The connectors typically are inserted into couplers mounted in the panel into which connectors or individual fibers are inserted from the rear side of the panel. Typical of such arrangements is that shown in U.S. Pat. No. 5,274,729 of King et al., for optical fiber connections. It can be appreciated that the cable leading up to the front of the panel affords protection from sharp bends for the individual fibers and only short lengths of unprotected fibers that are necessary to reach the different couplers are exposed. Thus, there is little likelihood that the fibers may be kinked or bent too sharply. On the other hand, however, the individual fibers leading away from, or up to, the rear of the panel are essentially unprotected. If these latter fibers are allowed to hang loosely from the rear of the panel, they are in danger of becoming bent, twisted, kinked, or otherwise stressed, with a consequent degradation of signal transmission, especially when an installer, for example, is working at the rear of the panel and making numerous connections and disconnections. In addition, there are numerous instances where fiber connectors, such as the SC type connector, are used in the field without benefit of, for example, a patch panel. Regardless of the milieu in which the connector is to be used, it is most desirable that some form of protection from the stresses be afforded the fiber.
The prior art is replete with arrangements for relieving, or protecting, the fiber from, stresses which night impair signal transmission. Thus, in U.S. Pat. No. 5,181,267 of Gerace et al. there is shown an optical fiber connector which has an elongated, exteriorly tapered strain relief boot extending from the rear of the connector and through which the cable passes. The boot slips over the rear end portion, i.e., the sleeve, of the connector, and protects the cable from excessive bending at the region where it enters the connector. Such a bolt arrangement, under heavy side loading, can be bent excessively, hence, it does not fully protect the fiber cable from such bending. In addition, the exit end, i.e., the end remote from the connector, does not prevent excessive bending of the cable. The boot of the Gerace et al. patent is typical of prior art boots in having a tapered outer diameter and a plurality of bend-limiting segments separated from each other by gaps of a width approximately equal to the width of each segment. When the cable is bent, the segment portions on the inside of the bend are forced toward each other until they touch, thereby preventing further bending. Properly designed, the boot prevents the cable from approaching the critical bend radius for the fiber or fibers therein.
Such bend limiting boots, where overall size and length are not constraints, can be capable of handling a wide range of loads or stresses. However, as a practical matter, the diameter of the boot should approximate that of the connector where they join, and that of the cable at the distal or remote end, and the length should be reasonably short because of space limitations and the like.
In U.S. Pat. No. 5,461,690 of Lampert, there is shown a bend limiting boot which, although complying with practical dimensional restraints, is still capable of providing a large measure of protection to the cable and fiber against side stress loads. The boot attaches, at one end, to the connector and has an outside diameter comparable in size to the connector, and has an axial bore for holding an optical fiber or cable. The boot is made of a material that is sufficiently flexible to permit bending, but sufficiently stiff to accommodate side loads. Transverse grooves are provided in the back half of the boot to accommodate light side loads while effectively limiting the bend radius of the fiber contained therein. The exit end of the boot, however, does not prevent sharp bends, i.e., bends of a radius less than the critical bend radius of the fiber, and the boot itself must, for proper operation, be fairly long.
Another type of prior art strain relief boot is shown in U.S. Pat. No. 5,261,019 of Beard et al. That boot is an elongated, tapered number attached to the rear of the connector, and having a plurality of transverse grooves to limit bending. This structure is similar to a large number of boots commonly in use. As is the case with the Lampert strain relief boot, there is no protection against fiber bending at the exit end of the boot, and the boot itself is quite long.
The Gerace et al. boot, discussed hereinbefore, is objectionable for the same reasons as the foregoing boots.
There are numerous other examples of strain relief boots, in one form or another, as shown in U.S. Pat. Nos. 4,812,009 of Carlisle et al., 5,073,044 of Egner et al., 5,151,962 of Walkes et al., and 5,212,752 of Stephenson et al. Seemingly all of the prior art strain relief boots are deficient in one or more of the following. In virtually all cases, the boots are too long, and project away from the patch panel, for example, a distance that interferes, for example, with the closing of the panel door which can cause acute bending of the fibers. Most of the boots are custom designed to fit one particular connector, and many of them are made of flammable material, such as PVC, which introduces and added drawback when used in customer premises.
There have been various approaches to alleviating or eliminating some, if not all, of the foregoing drawbacks. Thus, in U.S. Pat. No. 5,530,787 of Arnett, there is shown a curved fiber guide for supporting and protecting optical fibers extending away from the connector. The guide, which is made of a fairly stiff plastic material has, at one end, a mounting member for mounting the guide to any one of a number of different fiber bearing components, and its curvature is such that the fiber is prevented from kinking or being curved to a radius less than the critical radius of curvature. Such a guide solves many of the foregoing problems, but is only usable where there is ample space or room, inasmuch as it extends a considerable distance from the connector end from which the fiber is emergent.